Final answer:
Symbiosis is a close relationship between organisms of different species where at least one organism benefits. In the case of pathogenic microorganisms and their hosts, they have a parasitic relationship because the microorganisms benefit by causing harm or disease to the host.
Step-by-step explanation:
Symbiosis is a close relationship between two organisms of different species in which at least one of the organisms benefits. There are three types of symbiotic relationships: mutualism, commensalism, and parasitism. Mutualism is when both organisms benefit, commensalism is when one organism benefits without affecting the other, and parasitism is when one organism benefits at the expense of the other. In the case of pathogenic microorganisms and their hosts, they have a parasitic relationship because the microorganisms benefit by causing harm or disease to the host.